1. Field of the Invention
This invention relates to a sheet feeding apparatus for separating a plurality of original sheets stacked on a supply tray into a single sheet and for feeding them to a predetermined sheet processing location. The invention also relates to an automatic document feeder that uses the same.
2. Description of the Related Art
An image reading apparatus is designed to optically scan images on an original sheet, convert those images to electronic data and then transmit the data to an image forming apparatus such as a personal computer, facsimile machine or a copier.
Types of methods used to read image data on original sheets in such image reading apparatuses include a stationary document reading method that is a method of moving an optical reading system to acquire image data on a stationary document placed on a reading platen comprised of a clear glass, and a moving document reading method that is a method of using an automatic document feeder (hereinafter referred to as ADF) to separate a plurality of original sheets placed upon a supply tray to feed the original sheets one by one to read image data thereupon.
The ADF is provided with separating means to align leading edges of original sheets placed upon a supply tray, separate them and draw out the uppermost sheet one at a time. A variety of such original sheet separating means have conventionally been introduced and used in the past.
FIG. 10 shows a basic principal of sheet separating means of the prior art. Such mechanisms commonly employ a guide member 503 comprised of an oblique wall surface at a leading end of a tray that stores original sheets. Leading edges of the original sheets stacked against the guide member 503 abut against the oblique surface of the aforementioned guide member 503 thereby staggering and shifting the leading edges of the sheets from front to rear in a feeding direction. The sheets stacked on the tray are separated due to this shift in the front to rear direction and fed to a supply roller 508 side. In the sheets gripped and led between the supply roller 508 and a separation pad 504 which are vertically opposed to each other, the supply roller 508 applies a drawing force on the top sheet to move forward (left direction in the drawing). The second and below sheets are pulled by this force, but prevented from moving forward by the friction of the separation pad 504, thereby allowing only a single sheet to be drawn and supplied in the forward direction. It is also known in the prior art to use a separation roller instead of the aforementioned separation pad 504 to rotate in an opposite direction to the supply roller 508.
Prior art pertaining to such separating mechanisms is disclosed in, for example, Japanese Utility Model Publication (KOKAI) No. 5-83771 and Japanese Patent Publication (KOKAI) No. 10-316265.
Thus, the conventional apparatus for separating stacked original sheets is composed of a feed roller such as a supply roller or a belt, a separation pad pressed against the feed roller and a separating member such as a separating roller. A guide member is provided on the tray so that leading edges of the original sheets abut against an oblique surface to shift the edges in a front to rear direction. However, the prior art has the following problems.
Although the aforementioned guide member should be made of a material having an optimum coefficient of friction to shift leading edges of the original sheets in the front to rear direction, they are conventionally integrated with a tray and made of the same material. Thus, optimum separation is not achieved thereby causing jam or double-feed at the supply roller.
Furthermore, even when a material different from that of the tray is used for the guide member, normally the guide member is required to have a surface with a high coefficient of friction by using materials such as rubber or a specially formed synthetic resin, and an elastic member to attain more preferable separating effect. When materials with a high coefficient of friction are used, these materials tend to wear due to prolonged usage of the apparatus, requiring an occasional replacement of the part. Paper dust sticking to the sheets is known to extremely accelerate the material wear. The conditions of replacement are the same for the separating member described above. Both the guide member and the separating member need to be designed for replacement at an appropriate time.
When these two members, namely the separating member and the guide member, are freely removably mounted to an apparatus frame so that they can be replaced independently due to the need to replace these parts, a new problem such as a jamming problem caused by an error in positioning of the components occurs. A structure for freely removably mounting the two parts to the apparatus frame creates complexity in the apparatus.
It is a first object of the present invention to provide a sheet feeding apparatus in which a slanted guide member that shifts the original sheets stacked on the tray at a distal end of a tray in a front to rear direction, and the separating member, which separates the original sheets one by one, can be respectively made of optimum materials, achieving easy mounting and removal of the two members for replacement.
Another object of the present invention is to further facilitate replacement operation by mounting an integrated holder, in which a guide member and the separating member are integrally assembled to a frame.
Still another object of the present invention is to provide an automatic document feeder incorporated with the sheet feeding apparatus described above.
The aforementioned objectives can be achieved through the following structures.
To feed a sheet separately, a sheet feeding apparatus comprises a feeding roller, which touches the uppermost surface of the sheets stacked on a sheet supply tray to send out the sheet, and a sheet supply roller to press and supply the drawn out sheet. Components are at least one frame; a sheet stacking tray mounted to this frame; a paper feed rotating body or member which feeds sheets and is disposed at a downstream side of the stacking tray in a sheet feeding direction; a separating member which abuts against the paper feed rotating body to prevent more than one sheet from passing therethrough; urging means for pressing the separating member to the paper feed rotating body; a guide member having an oblique surface to shift leading edges of the sheets and disposed at a leading end of the stacking tray in the sheet feeding direction; a holder member mounted with the separating member and the guide member; and fastening means to freely detachably fasten a separation unit, which is formed of the separating member, the guide member and the holder member, to the frame.
In other words, the guide member and the separating member are mounted to the single holder member that is freely removably fastened to the frame, so that the guide member and separating member are easy to be replaced at any time without requiring adjustment of their mutual mounting positions.
Furthermore, the aforementioned frame can be made of a metallic chassis, or can be a unitized body dually using an apparatus housing as the frame. A spring or some other urging means can be used to fix the fastening means to the frame by pressing against a stopper formed on a portion of the frame.